1. Field of the Invention
The present invention relates to nail and screw type fasteners. More specifically, the invention is a reverse barb system for screws and nails that provides screws and nails with a resistance to backing out or popping out from a workpiece.
2. Description of the Related Art
A problem exists in construction wherein the fasteners used in wood frame construction, particularly screws and nails, tend to come loose over time. Subjected to weight, expansion and contraction of materials due to changing temperature and humidity, vibration, the force of storms, and other stresses, the screws and nails used to join wood and other materials in construction have a tendency to back out. Nails simply work back out as if pulled out, while screws tend to turn out over time, their threads following the thread path of entry. As the screws and nails back out, the joints that they fasten become loose, leaving structures weak and vulnerable to further damage, or even collapse. Nothing is more common than to see nail or screw heads popping out from drywall as the fasteners used to secure drywall to wood studs loosen over time.
The lifespan and structural integrity of a structure held together by screws and nails can be improved by the use of screws and nails that resist the tendency to back out. A few previous fasteners have been fashioned with features provided to resist the tendency of the fastener to back out.
U.S. Pat. No. 4,973,211, issued on Nov. 27, 1990 to F. Potucek, discloses a star-shaped fastener that is essentially a nail having at least three fins radiating from a central shaft. The fins run the length of the nail, and provide additional surface area while using less material for their construction. The increased surface area provides additional friction and tends to increase the fastener's resistance to backing out. Additionally, an embodiment of the star fastener includes several small barbs disposed along the shaft in between the fins. The barbs are intended to increase the back-out resistance of the fastener. However, the barbs are quite small relative to the cross section of the fastener. Additionally, the barbs are in-line with one another. Since the fastener has no tendency to turn as it is driven into place, the barbs may withdraw through the channel that they cut into the wood as the fastener is driven. Although wood fibers will tend to return to their original position after the fastener is driven into place, they are not likely to fully close in behind the barbs. The effectiveness of the barbs to reduce back-out is thus decreased.
U.S. Pat. No. 3,969,975, issued on Jul. 20, 1976 to H. Krol, discloses a heavy-duty staple that has a series of anchoring notches along the prongs of the staple. The anchoring notches function essentially as barbs, tending to hold the staple from backing out. Again, however, the barbs cannot have their full gripping effect when they will back out along the same path through which they were inserted.
U.S. Pat. No. 5,230,597, issued on Jul. 27, 1993 to J. Nuttall, discloses a fastener comprising an elongated shank that is provided with at least one wedge-shaped protrusion along the shank. This wedge functions as a barb, allowing the fastener to be freely driven into place but tending to prevent the fastener from backing out. Unlike the barbs of the previously discussed fasteners, however, the wedge is angled so that the fastener turns slightly as it is driven. The result of this turning action is that the wedge provides greater resistance to back-out along a straight path. This fastener, however, lacks a sharp point. Not a general purpose fastener or nail, the fastener is intended for insertion into a predrilled hole. The wedge is welded along the fastener's shank. This method of manufacture of the fastener is not suitable for nails, which are typically formed by a cold-forge process.
U.S. Pat. No. 5,557,898, issued to T. Dixon on Sep. 24, 1996, discloses a barbed finish nail having a plurality of flexible barbs along its shank. The barbed finish nail is used to fasten trim pieces to a wall construction of wallboard and metal studs. Metal studs are typically formed of sheet metal, formed to roughly the contour and dimensions of a two-by-four stud. The flexible barbs of the barbed finish nail are designed to expand as the nail is driven through, and then exits, the sheet metal material of the metal stud. The expanded barbs catch against the inner surface of the metal stud to resist withdrawal. While effective for its purpose of fastening trim pieces to a wall construction of wallboard and metal studs, the flexible barbs of the barbed finish nail are not useful as a general-purpose construction nail.
U.S. Pat. No. 5,253,965, issued on Oct. 19, 1993 to J. Angel, discloses a barbed fastener for joining two or more plastic or metal panels. The fastener has large barbed fins extending along the fastener's shank. This specialized fastener includes an adhesive, contained in a groove formed along the fastener shank, to help to hold the fastener in place.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus a reverse barb system for screws and nails solving the aforementioned problems is desired.